Caster switch unit for carry-and-transport device

Abstract

A carry-and-transport device includes a caster unit and a straight-wheel unit. A control unit which has a sleeve and the sleeve is located corresponding to the straight-wheel unit of the carry-and-transport device. A movable frame is connected to the sleeve and has an auxiliary caster unit connected to the lower end thereof. The auxiliary caster unit normally located above the ground and does not contact the ground. A switch unit is connected to the top of the movable frame so as to control the movable frame to move upward and downward. When the carry-and-transport device turns or makes a U-turn, the auxiliary caster unit touches the ground by operation of the control unit so as to reduce the turning radius of the carry-and-transport device.

What is claimed is: 
     
         1 . A carry-and-transport device comprising:
 a caster unit and a straight-wheel unit;   a control unit having a sleeve which is located corresponding to the straight-wheel unit, a movable frame connected to the sleeve and having an auxiliary caster unit connected to a lower end thereof, the auxiliary caster unit being normally located above the ground, and   a switch unit connected to a top of the movable frame which controls the movable frame to move upward and downward.   
     
     
         2 . The carry-and-transport device as claimed in  claim 1 , wherein the carry-and-transport device is a transportation cart, a manual cart or a bed. 
     
     
         3 . The carry-and-transport device as claimed in  claim 1 , wherein the switch unit of the control unit is a lever. 
     
     
         4 . The carry-and-transport device as claimed in  claim 1 , wherein the switch unit of the control unit is a hydraulic cylinder, a pneumatic cylinder or an electric cylinder.